In the field of bearings, it is known to use a tachometer in order to determine a rotation parameter, such as a rotation speed, of a rotating part supported by a bearing with respect to a non rotating pai-t. As explained in EP-A-1 933 155 , one can use an encoder washer with magnetic poles fast in rotation with a rotating ring of a bearing, and one or several sensors distributed in a sensor body around the encoder washer or located in front of it. Such a sensor body is fed with electric power via a cable which is connected to the sensor body, generally to a printed circuit board which holds the sensors and some other electronic components within the sensor body. This cable can also be used to convey the output signals of the sensors towards an electronic control unit located outside the sensor body. Such a cable is provided, at a free end opposite to the sensor body, with a connector for connection to a power supply and/or to a network for distributing electronic signals. Depending on the intended use of the sensor unit, the cable has a length which generally varies between 250 and 850 mm and the connector is adapted to the environment of the sensor unit.
Such a cable prevents, to a large extent, automation of the manufacturing process of sensor units insofar as, when several sensor units are stored in a box, their respective cables tend to interweave. Moreover, when one holds a sensor unit by its sensor body, the cable and the connector tend to hang on a side of the sensor unit. It is thus difficult for a robot to grasp and move a sensor unit on a production line for instrumented bearing assemblies. The cables of the known sensor units are also cumbersome for the operators who have to install such sensor units on some bearings, in order to build instrumented bearing assemblies.